The present invention relates to neutralization processes and more particularly the present invention relates to the neutralization process of halogen silicone compounds generally and more specifically, chlorosilanes.
Fluorosilicone compounds are well known. Such compounds have the advantage of solvent resistance and they are utilized to form rubber parts or elastomeric parts where the parts come in contact with very solubilizing solvents. In particular such fluorosilicone compounds also include fluorosilicone fluids having a viscosity varying from 50 to 1,000,000 centipoise at 25.degree. C. where the fluorosilicone fluids are utilized as hydraulic fluids as fluorosilicone greases and channel sealants. The fluorosilicone greases and channel sealants have the advantage of solvent resistance as mentioned previously.
In the past, it was usual to make the fluorosilicone fluids by equilibrating fluorosilicone substituted cyclic trisiloxane with low molecular weight, triorganosilyl end-stopped chainstoppers in the presence of alkali metal hydroxides or more preferably, a strong acid. The resulting mixture equilibrated to form a linear fluorosubstituted diorganopolysiloxane polymer having a viscosity of anywhere from 50 to 1,000,000 centipoise at 25.degree. C. However, there was one disadvantage of the equilibration process and particularly because the low molecular weight triorganosilyl end-stopped chainstoppers would go into the polymer only very slowly such that there resulted a formation of high amounts of cyclics at the terminal point of the equilibration reaction. Accordingly, the yield of the triorganosilyl end-stopped diorganopolysiloxane fluid was not as high as desired. There has been developed an improvement to such a process as disclosed in the patent application of Ben A. Bluestein entitled "Process for Synthesizing Silanol End-Stopped Fluorosilicone Fluid, " Ser. No. 92,800 and as disclosed in the patent application of Ben A. Bluestein entitled "Process for Producing M-Stopped Silicone Fluids From Silanol Fluids, " Ser. No. 92,920 which are incorporated into the present case by reference. These dockets disclose a novel way for producing a triorganosilyl end-stopped linear diorganopolysiloxane fluid. The process disclosed comprises taking an appropriate fluorosubstituted cyclotrisiloxane and and reacting it with small amounts of water as a chainstopper, in the presence of an alkali metal hydroxide catalyst and polyethylene glycol dimethyl ether as a promotor. The process results in the formation of a linear silanol end-stopped diorganopolysiloxane polymer of a viscosity of 50 centipoise to 1,000,000 centipoise at 25.degree. C. in very rapid fashion and at a very high yield. After the desired polymer has been formed, which may take place any where from 1 to 6 hours, the catalyst is neutralized with a suitable acidic agent such as a chlorosilane or a silyl phosphate as disclosed in the foregoing patent applications. The resulting silanol end-stop polymer is then taken and is reacted with a triogranohalogensilane which is preferably a triorganochlorosilane so as to chainstop or replace the silanol groups in the polymer with triorganosilyl groups. This reaction also results in high yield of the desired product. There is only one difficulty with this process and that is, it is desirable to use excess triorganochlorosilane so as to insure that all the silanol groups are terminated or replaced by triorganosilyl chainstopping groups. This causes another disadvantage in that excess chlorosilane is difficult to remove from the fluid. If it is not removed from the fluid, it makes the fluid acidic and causes it to revert or degrade upon standing. Accordingly, the excess halogen silane has to be neutralized to less than 50 and preferably less than 10 parts per million of acid. As disclosed in the foregoing patent applications, an alkali metal hydroxide is not desirable since it creates undesirable salts which might require filtration. Also, there could be utilized to neutralize the halogen silicone compound or chlorosilane soda ash and water as disclosed in the above patent applications. Although such an addition of soda ash and water would neutralize the chlorosilane, it creates a precipitate which has to be filtered out which filtration step is not necessarily desirable in many plant operations. Alkali metal hydroxide could be utilized, however, that creates alkali metal salts in the polymer which tend to degrade it under certain conditions. Accordingly, it is highly desirable to convert the excess chlorosilane to species wherein the chloride could be removed from the polymer by distillation at elevated temperature.
It should be noted that while the above neutralization process was mentioned or discussed in terms of production of fluorosilicone fluids such neutralization of chlorosilanes can be present or necessarily desirable in many silicone manufacturing operations. Accordingly, although the necessity in the neutralization step of excess chlorosilanes was mentioned above with respect to chlorosilanes in the production of fluorosilicone fluids, it must be understood that such a neutralization step may be necessary in any silicone process in which excess chlorosilanes are present and in which it is necessary to neutralize the excess chlorosilanes. Accordingly, if it is desired for one reason or another to neutralize the excess chlorosilanes, then it is desirable to utilize a neutralization step which will neutralize the chlorosilanes without requiring a filtration step and without the formation of inorganic salts which would degrade the final product as well as be difficult to separate from the final product.
It is known that orthoformates react with chlorosilanes to produce alkylchlorides, alkylformates and alkoxysilanes all in the same reaction. It is also known that catalysts such as aluminum chloride and zinc chloride are useful and necessary for completing these reactions. However, in the case where the final product is a polymer or a residue as described above, it is not desirable to utilize these metal chlorides with orthoformates to effect conversion of excess chlorosilanes to distillable species because of the deleterious effects of the metal chloride on the polymer or residue.
Accordingly, it is one object of the present invention to provide a process for neutralizing excess halogen silicone compounds.
It is an additional object of the present invention to provide a process for neutralizing or removing excess chlorosilanes so as to produce species which may be distilled off with degrading the polymer.
It is yet an additional object of the present invention to provide a novel process for neutralizing excess chlorosilanes in the production of fluorosilicone polymers.
These and other objects of the present invention are accomplished by means of the disclosure set forth herein below.